Chitosan is a linear copolymer of N-acetyl-D-glucosamine and D-glucosamine linked by glucosidic linkage. Chitosan may be derived from chitin, which is the second most abundant natural polymer. Chitosan is formed through N-deacylation of the chitin molecule. Chitin is found in the exoskeleton of shellfish such as shrimp, lobster, and or crabs. Chitin may also be found in the exoskeleton of insects.
Chitosan may also be used as a precursor for value-added polymers in biomedical and pharmaceutical areas due to the non-toxic aspect of chitosan. Chitosan has also shown some biologic activity, as well as biocompatibility, biodegradability, and/or potential of physical and chemical modification.
Some attention has been placed on the modification reaction of chitosans to construct sophisticated molecular architecture having various advanced functions. High molecular weight chitosans, generally averaging at least 10,000 Daltons, have been prepared as functionalized nanoparticles and have been reported to have pharmaceutical and medical applications. However, chitosan is generally very difficult to modify chemically due to the strong inter and intra molecular hydrogen bonding. As a result, high molecular weight chitosan has been modified under heterogeneous conditions due to the poor solubility of chitosan in organic solvents, generally leading to a low degree of substitution and low yield of functionalized chitosan products.